1. Field of the Invention
This invention relates to rotationally stabilized contact lenses.
2. Prior Art Statement
A. Lens Product
The Barron contact lens patents (U.S. Pat. Nos. 3,698,802 and 4,084,890) disclose the use of contact lenses with a thickened peripheral region to prevent shifting or rotation of the lens used as astigmatism lenses. These patents also teach that when it is found that the upper lid of a user of lens exerts an extraordinary force against the lens, which force would tend to shift the lens, additional adherence can be created by adding weight to the lens at the 6 o'clock position thereof. These lenses have an increased thickness of material which is generally semi-ring-shaped as viewed in plan and wedge-shaped in cross-section.
Fanti, U.S. Pat. No. 4,095,878 and The Optician, No. 169, beginning at page 8 (April 4, 1975), disclose flattening the lens along a portion of its peripheral region to stabilize a soft contact lens, which may be symmetrical or asymmetrical to its axis of rotation, in a predetermined orientation. This orientation is necessary if astigmatism, heterophorias or squinting are to be corrected. The lens may have a complimentary flattened area on the opposite periphery. The lens has a flattened region on the outer surface along at least one portion of its periphery, extending substantially in parallel to the central axis of the lens. That is, the lens has a minimum thickness at the position 12 o'clock and increases in the direction of 9 o'clock and 3 o'clock, the points of maximum thickness should be at 9 o'clock and 3 o'clock. No carrier for the lens is disclosed.
Strachan et al, Canada No. 1,004,889, disclose the stabilization of contact lenses where at least one surface of the lens is toric by the adding of any one of, or a combination of, single truncation, double truncation and prism ballast features to the lens. The truncation can be either horizontal or vertical, with the vertical truncation being preferred when the lens is thicker.
Brummel et al, U.S. Pat. No. 4,211,476, disclose contact lenses with angular orientation and stabilization by locating between the prescription zone of the lens and the periphery of the lens means for forming a control meniscus with the tear layer of the eye so that the resultant vector of the fluid forces created by the means falls within an arcuate area defined by the gravity vector passing through the geometrical center of the lens and 15.degree. on eitber side of the vector. The control meniscus forming means can be a hold with countersinks on the anterior and posterior surfaces of the lens.
U.K. patent application No. 2,031,178A discloses rotational stabilization of a soft contact lens having a central optic zone and a peripheral zone, characterized in that the peripheral zone comprises (a) a sink segment formed by a depression in the anterior face, the sink segment being defined by a line joining two points on the circumference of the peripheral zone, and (b) a secondary segment diametrically opposite the sink segment, a secondary segment having a lower mass than the sink segment. The secondary segment can be an area of the face of the peripheral zone directly opposite the sink segment which has been mechanically cut away by eccentricity establishing a secondary arc which defines with the circumference a secondary segment of reduced weight and thickness. The sink segment can be defined by a visible cord instead of an arc.
VanderKolk et al, European patent application No. 0008,726, disclose stabilizing toric contact lenses. A high minus powered anterior surface toric lens is made having a toric central optical portion without prism and an annular outer portion having prism but without toric effect, the outer portion being truncated in a lower part so that there is upward movement of the center of rotation of the blank and of the center of gravity in a manner such that the center of gravity is in use below the center of rotation, thus assisting if the lens is rotated by lid or eye movement the lens tends to rotate back into correct orientation.
Other patents illustrative of prior art means for stabilization of contact lenses include U.S. Pat. Nos. 3,102,157; 3,211,810; 3,246,841; 3,431,327; 3,933,411 and 4,071,293.
B. Processes
Neefe, U.S. Pat. No. 4,202,848, discloses a method of making bifocal contact lenses by molding the plastic lens to form its concave surface, mounting the combined lens and mold on an off-center lathe to produce a prism lens, removing the lens from the lathe, turning the lens 180.degree., replacing the lens on the off-center lathe and cutting the near power segment.
Wichterle, U.S. Pat. Nos. 3,408,429, 3,496,254 and 3,660,545 disclose the spincasting process for preparing contact lenses. The polymerizing mixture is contained in a rotating open mold having a concave surface. The anterior, convex surface of the lens, is thus formed by the mold surface, and the posterior, concave surface of the lens, is formed as the result of centrifical forces, surface tension of the polymerizing mixture and other factors such as the size and shape of the mold, the volume of the polymerizing mixture, the condition of the mold's surface, etc. The concave surface of the lens thus formed is approximately parabolic in shape and many factors must be carefully controlled to produce reproducable shapes. Lenses produced by the spincasting usually require postpolymerization edge finishing.
Clark et al, U.S. Pat. No. 4,197,266, disclose apparatus for and method of forming ophthalmic lenses including contact lenses. In operation the plastic lens material maintained in a flowable state is transferred from the reservoir to the mold cavity where it is formed into a permanent shape. Thereafter selected portions of the cast lens are removed as necessary or expedient.
Wichterle, Australia No. 295,538, discloses a method of making hydrogel copolymer contact lenses consisting of copolymerizing a solvent-free monomer mixture capable of forming three dimensional hydrophilic copolymers in a rotating mold, working the hard, non-swelled lens thus obtained, if necessary, washing it and then swelling the product to obtain the final lens. The method allows also to provide special shapes to compensate astigmatic deviation of the eye. Mechanical working of the lens is made possible by the fact that the copolymer containing no appreciable amount of a swelling liquid is comparatively hard and can be easily cut and polished.
Other patents illustrative of prior art procedures and equipment for manufacture of toric contact lenses include U.S. Pat. Nos. 3,079,737; 3,344,692; 3,482,906; 3,535,825; 3,623,800 and 3,950,082.